Hank, the most common problem of cruise control failure is the amplifier
unit... it is located under the dash near your brake pedal... I have the
same problem too and will attempt to repair this also.
They say the most common problem is the solder crack... so I am taking a
guess it is at the plug to ciruit board connection. So reflowing should do
Mercedes Benz Club of America has an excellent article about troubleshooting
Let me know how you make out... because I have to do the same on two cars.